Types of reactors may be divided according to a configuration of a safety system and installation locations of main components. First, reactors are divided into active reactors using active power such as a pump, and passive reactors using passive power such as a gravity force, gas pressure or the like according to the configuration of the safety system. Next, reactors are divided according to the installation locations of the main components into loop type reactors (for example, Korean pressurized water reactor) in which main components (a steam generator, a pressurizer, a pump impeller, etc.) are installed at an outside of a reactor vessel, and integrated type reactors (for example, Korean SMART reactor) in which the main components are installed at an inside of the reactor vessel.
In general, a containment structure for protecting an outside of the reactor vessel (or reactor coolant system of a loop type reactor) is referred to as a containment building (or reactor building) when the structure is constructed using reinforced concrete, and as a containment vessel (safeguard vessel for a small structure) when the structure is manufactured using a steel. In this specification, the containment building, the reactor building, the containment vessel, the safeguard vessel and the like, unless otherwise specified, are commonly referred to as “containment.”
In a nuclear power plant industrial field, a passive containment cooling system (or containment cooling system) is widely used as a system of maintaining soundness of the containment by reducing pressure in a manner of condensing steam and cooling internal atmosphere, when internal pressure of the containment increases due to a discharge of coolant or steam, which results from a loss-of-coolant accident or steam line break accident occurred in various reactors including such integral reactor. As methods used for similar purposes to the passive containment cooling system, a method using a suppression tank in which steam discharged into the containment is induced into the suppression tank and condensates the steam (Commercial BWR, CAREM: Argentina, IRIS: U.S. Westinghouse, etc.), a method of applying a steel containment vessel and cooling (spray, air) an outer wall (AP1000: U.S. Westinghouse), and a method using a heat exchanger (SWR1000: Framatome ANP of France, AHWR: India, SBWR: GE of USA) and the like are currently used. A shell and tube type heat exchanger or condenser (SBWR: GE of USA, etc.) is generally applied as a heat exchanger of a passive containment cooling system related to the present invention, and the heat exchanger depends on natural circulation.
In the nuclear power plant industrial field related to the present invention, a residual heat removal system (auxiliary feedwater system or passive residual heat removal system) is employed as a system for removing heat of the reactor coolant system (sensible heat in the reactor coolant system and residual heat of the core) when an accident occurs in various nuclear power plants including the integral reactor.
Among those residual heat removal systems, two methods, such as a method of directly circulating primary coolant of the reactor coolant system to cool a reactor (AP1000: U.S. Westinghouse) and a method of indirectly circulating secondary coolant using a steam generator to cool a reactor (SMART reactor: Korea) are mostly used as fluid circulation methods of the passive residual heat removal system using natural circulation based on a density difference between steam and water, and a direct condensation method of injecting primary coolant into a tank (CAREM: Argentina) is partially used.
Furthermore, as methods of cooling an outside of a heat exchanger (condensation heat exchanger) of the passive residual heat removal system, a water-cooling method (AP1000) applied to most of reactors, some air-cooling methods (WWER 1000: Russia), and a water-air hybrid cooling method (IMR: Japan) are currently used. A heat exchanger of the passive residual heat removal system performs a function of transferring heat delivered from a reactor to an outside (ultimate heat sink) through an emergency cooling tank or the like, and condensation heat exchangers using a steam condensation phenomenon with excellent heat transfer efficiency are widely employed as a heat exchanger type.
In relation to the present invention, a printed circuit heat exchanger has been developed by the Heatric Ltd. in UK (U.S. Pat. No. 4,665,975, 1987), and is very variously used in general industrial fields. The printed circuit heat exchanger is a heat exchanger having a structure in which welding between plates of the heat exchanger is removed using a dense flow channel arrangement by a photo-chemical etching technique and diffusion bonding. Accordingly, the printed circuit heat exchanger is applicable to high-temperature and high-pressure conditions and has high accumulation and excellent heat transfer efficiency. The advantages of the printed circuit heat exchanger, such as durability against the high-temperature and high-pressure environments, the high accumulation and the excellent heat transfer efficiency, extend an application range of the printed circuit heat exchanger to various fields, such as an evaporator used in a very low temperature environment and the like, a condenser, a cooler, a radiator, a heat exchanger, a reactor, an air conditioning system, a fuel cell, a vehicle, a chemical process, a medical instrument, nuclear power plant, an information communication device.
Meanwhile, a plate type heat exchanger, which is to be used as one of examples according to the present invention, has been widely applied in industrial fields over one hundred years. The plate type heat exchanger is generally configured such that plates are pressed out to form flow channels and then the pressed plates are joined to each other using gaskets or by typical molding or brazing. Accordingly, the plate type heat exchanger is similar to the printed circuit heat exchanger in view of an application field, but is more widely used under a low-pressure condition. Heat transfer efficiency of the plate type heat exchanger is lower than that of the printed circuit heat exchanger but higher than that of the shell and tube type heat exchanger. Also, the plate type heat exchanger is manufactured through more simplified processes than the printed circuit heat exchanger.
The plate type heat exchanger disclosed herein, unless otherwise specified, is referred to as a heat exchanger when a difference is present in a method of manufacturing or bonding plates as well as the general plate type heat exchanger and the printed circuit heat exchanger.
Meanwhile, thermoelectric phenomena involving a thermoelectric element or thermoelectric power generation disclosed herein include a Seebeck effect (1822), Peltier effect (1834), Thomson effect (1854) and the like. The Seebeck effect means a phenomenon in which electromotive force (electric power) is generated to cause a passage of the current when temperature difference exists between two contacts of a closed circuit formed by connecting two kinds of metals or semiconductors. This current is referred to as a thermoelectric current, and the electric power generated between metal lines is referred to as thermoelectromotive force (thermoelectric power). The magnitude of the thermoelectric current depends on the kinds of the paired metals and the temperature differences between the two contacts, and additionally is dependent on electric resistance of the metal lines. The Peltier effect, unlike the Seebeck effect, is a phenomenon in which the temperature difference is generated due to production and absorption of heat at two junctions when a current is applied. The Thomson effect is a phenomenon in which the Seebeck effect and the Peltier effect have correlation. A thermoelectric generator which is an energy conversion device of directly converting heat energy into electric energy can generate electricity (electric power) for use without a mechanical driving component when a heat source exists. The thermoelectric generation uses the Seebeck effect, in which electromotive force is generated due to a temperature difference between both ends of two different metals connected to each other, to cause the passage of the current by the production/absorption of heat of a thermoelectric module. The thermoelectric generation technology is a practical technology capable of reusing even low grade waste heat as electricity by converting even heat near room temperature into electricity, and is applied to an ocean thermal energy conversion (OTEC) power generation, a solar energy generation and the like. Accordingly, a usage range of the thermoelectric generation gradually becomes wide.
The passive safety system for the nuclear power plant uses natural force that is generated by natural phenomena such as gravity force, gas pressure, density difference and the like, and thereby constructing the system is very limited. The passive safety system is driven using natural force by operating a safety system using power of a small battery required for opening a valve or the like when an emergency AC power source or an external power supply is not present. Therefore, the passive safety system is very excellent in view of safety. However, economical efficiency thereof is highly likely to be decreased due to a very limited design configuration option and very low driving force. For the heat exchanger, for example, a circulation flow of internal or external fluid of the heat exchanger depends on a natural circulation typically caused by a density difference. Accordingly, a heat exchange performance is decreased and thereby a size of the heat exchanger increases.
Therefore, a configuration of a system having a compact size and providing higher efficiency than efficiency obtained when using the related art heat exchanger, by supplying circulating force to fluid using electricity produced by thermoelectric generation in a manner of additionally employing a thermoelectric element in a heat exchanger, which can be used in a passive safety system of a nuclear power plant.